Field
This disclosure relates to a positive electrode composition for a rechargeable lithium battery, and a positive electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same.
Description of the Related Technology
A rechargeable lithium battery includes positive and negative electrodes including a material that can reversibly intercalate/deintercalate lithium ions as positive and negative active materials and an organic electrolyte solution or a polymer electrolyte solution filled between the positive and negative electrodes. Herein, the positive and negative electrodes intercalate and deintercalate lithium ions and produce electrical energy through oxidation and reduction reactions.
As for a positive active material of a rechargeable lithium battery, a lithium-transition metal oxide having a structure being capable of intercalating lithium ions such as LiCoO2, LiMn2O4, LiNii-xCoxO2 (0<x<1) and the like are mainly used.
As for an electrode binder used in a rechargeable lithium battery, a non-aqueous system is generally used, but a binder obtained by dissolving polyvinylidene fluoride (PVDF) in an N-methyl-2-pyrrolidone (NMP) or acetone as the organic solvent is particularly used.
However, when the non-aqueous system is used as a binder, the organic solvent such as NMP, acetone and the like may contaminate the environment and is also relatively expensive and thus, may increase the unit manufacturing cost of a lithium battery. In addition, since the PVDF has relatively weak adherence, the binder may be required in a large amount to apply a sufficient binding force between a current collector and an active material.
However, when the binder is used in a large amount, the amount of the active material is reduced accordingly, thus failing to achieve large capacity of a battery. In addition, fluorine of the PVDF reacts with lithium ions and forms LiF, which may cause thermal runaway and thus, decrease safety of the lithium ion battery. In particular, as the lithium ion battery is manufactured to have higher capacity, so does the thermal runaway of LiF and thus, makes it difficult to obtain a safe battery.
In order to solve the problem, an attempt to use an aqueous binder system obtained by dispersing a binder into water has recently been made during manufacture of an electrode. The aqueous binder as an emulsion may be dispersed into water without needing an organic solvent and also, has strong adherence and thus, may be required in a smaller amount and proportionately increasing the amount of an active material, thus achieving a high-capacity lithium battery.
However, the aqueous binder system requires improvement in terms of processibility of appropriately maintaining fluidity and viscosity of an electrode composition and the like, formation of a stable layer without brittleness when the electrode composition is dried, and the like.